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| author | Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> | 2012-05-03 22:14:14 +0200 |
|---|---|---|
| committer | Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> | 2012-05-07 16:21:13 +0200 |
| commit | b7e5ffe5d83fa40d702976d77452004abbe35791 (patch) | |
| tree | 65f50b54a7c974f5de0a27c9cd3c954e24a9c077 | |
| parent | xen/apic: Return the APIC ID (and version) for CPU 0. (diff) | |
| download | linux-b7e5ffe5d83fa40d702976d77452004abbe35791.tar.xz linux-b7e5ffe5d83fa40d702976d77452004abbe35791.zip | |
xen/pte: Fix crashes when trying to see non-existent PGD/PMD/PUD/PTEs
If I try to do "cat /sys/kernel/debug/kernel_page_tables"
I end up with:
BUG: unable to handle kernel paging request at ffffc7fffffff000
IP: [<ffffffff8106aa51>] ptdump_show+0x221/0x480
PGD 0
Oops: 0000 [#1] SMP
CPU 0
.. snip..
RAX: 0000000000000000 RBX: ffffc00000000fff RCX: 0000000000000000
RDX: 0000800000000000 RSI: 0000000000000000 RDI: ffffc7fffffff000
which is due to the fact we are trying to access a PFN that is not
accessible to us. The reason (at least in this case) was that
PGD[256] is set to __HYPERVISOR_VIRT_START which was setup (by the
hypervisor) to point to a read-only linear map of the MFN->PFN array.
During our parsing we would get the MFN (a valid one), try to look
it up in the MFN->PFN tree and find it invalid and return ~0 as PFN.
Then pte_mfn_to_pfn would happilly feed that in, attach the flags
and return it back to the caller. 'ptdump_show' bitshifts it and
gets and invalid value that it tries to dereference.
Instead of doing all of that, we detect the ~0 case and just
return !_PAGE_PRESENT.
This bug has been in existence .. at least until 2.6.37 (yikes!)
CC: stable@kernel.org
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
| -rw-r--r-- | arch/x86/xen/mmu.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c index b8e279479a6b..69f5857660ac 100644 --- a/arch/x86/xen/mmu.c +++ b/arch/x86/xen/mmu.c @@ -353,8 +353,13 @@ static pteval_t pte_mfn_to_pfn(pteval_t val) { if (val & _PAGE_PRESENT) { unsigned long mfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT; + unsigned long pfn = mfn_to_pfn(mfn); + pteval_t flags = val & PTE_FLAGS_MASK; - val = ((pteval_t)mfn_to_pfn(mfn) << PAGE_SHIFT) | flags; + if (unlikely(pfn == ~0)) + val = flags & ~_PAGE_PRESENT; + else + val = ((pteval_t)pfn << PAGE_SHIFT) | flags; } return val; |